A number of processes for preparing N-phosphonomethylglycine (hereinafter abbreviated to PMG) using N-phosphonomethyliminodiacetic acid (hereinafter abbreviated to PMIDA) as a starting material, using water as a solvent and using an oxidizing agent and a catalyst may be mentioned. Among them:
(a) a process in which, under ordinary pressure or under high pressure, molecular oxygen or gas containing said oxygen is used as an oxidizing agent and activated carbon is used as a catalyst is found in (1) Japanese Unexamined Patent Publication (KOKAI) No. Sho 50-160222, (2) Japanese Unexamined Patent Publication (KOKAI) No. Sho 56-18994 and (3) Japanese Unexamined Patent Publication (KOKAI) No. Sho 60-246328, (b) a process in which hydrogen peroxide is used as an oxidizing agent and an acid (an organic acid or an inorganic acid) is used as a catalyst is found in (4) Japanese Unexamined Patent Publication (KOKAI) No. Sho 49-48620 and (5) Japanese Unexamined Patent Publication (KOKAI) No. Hei 2-270891, and (c) a process in which hydrogen peroxide is used as an oxidizing agent and a metal compound is used as a catalyst is found in (6) Japanese Unexamined Patent Publication (KOKAI) No. Hei 4-224593, (7) Japanese Unexamined Patent Publication (KOKAI) No. Hei 4-210992, (8) Japanese Unexamined Patent Publication (KOKAI) No. Hei 4-224592 and (9) Japanese Unexamined Patent Publication (KOKAI) No. Hei 4-273885, respectively.
In the technique of (a), the reaction proceeds extremely slowly under ordinary pressure, whereas although the yield of the reaction is good under high pressure, pressure equipment is required. Further, it is necessary to pre-treat the activated carbon to be used. For these reasons, this technique leads to increase in cost.
In the technique of (b), an organic acid or an inorganic acid is used, so that the reaction apparatus might be corroded, and much time is required for disposal of the used acid.
In the technique of (c), a metal compound is used. Some metal compounds are harmful substances, so that disposal might be attended by difficulties or, when the possibility of contaminating the product PMG with a harmful catalyst is considered, a countermeasure should be taken in view of environmental problems.
Since the problems as described above are involved, it has been demanded to develop a safe and efficient preparation process.